Development of fiber optic sensing techniques for structural assessment

Fiber optic sensors are useful means for structural assessment. A novel damage detection sensor based on the use of a doped optical fiber to locate damage site in composite materials has been developed. The spatial accuracy of the sensor was experimentally determined as 2.86 mm over a sensing gauge of 425 mm. This technique does not require embedding a grid of optical fibers in the host structure or using the optical time domain reflectometry, which is employed by techniques reported previously.; For the structural compliance measurement, a low cost long gauge strain sensing system has been developed and applied to a few structural applications. The test results showed that this system not only worked accurately, but also demonstrated advantages over conventional techniques. For solving the lead-in/out fiber sensitivity problem of the sensor, a novel sensor was developed using broadband in-fiber Bragg gratings. Research was carried out from conceptual test to building a sensing system based on the design. This novel sensing system has been successfully used in a number of field applications for measuring structural strain or deformation. However, it requires the spectral overlap of two Bragg gratings and contains mechanical moving parts for the optical path length compensation. Improving this system led to the development of the novel long gauge length sensor based on laser wavelength tuning technique. This sensor is electro-optically demodulated, therefore, there are no mechanical moving parts involved. It retains the desirable features of the previously developed sensors, without requiring the spectral overlap of Bragg gratings. It also provides the potential of multiplexing in the wavelength domain.; For future development, the polarization effects on the long gauge length sensor and the possible solutions are discussed. Considerations of temperature effects and designs of sensing schemes for decoupling them from strain measurement are also presented.